3 Answers
3

The golden hour is the period of time (roughly an hour) immediately either side of sunrise/sunset. At this time the sun is very low in the sky. As a result the light passes through much more of the atmosphere. The result of this is that:

the high frequencies (blues) are filtered out giving a very warm light

the light is diffused by particles in the air, softening the light for softer shadows

the lighting angle is very low which gives great sculpting light, and long shadows

the intensity of direct sunlight is much reduced, allowing you to shoot into the sun without silhouetting.

All of this means you can grab images like this. The reduced intensity of the direct sunlight means the light from the rest of the sky is brighter by comparison, this provides a great soft fill in light, allowing the direct sunlight to be used as a back/rim light to accent shapes.

The term "golden" partially refers to the warm colour of the light, and partially to the fact that everything you shoot turns to gold during the golden hour!

+1 for a perfect image of the golden hour that's not a landscape!
– Nicholas SmithOct 3 '11 at 12:22

Thank you all, this is very helpful. Matt, I noticed you included before and after sunrise and sunset. I was thinking textures will be more pronounced before sunset but this is more comprehensive. Sorry, I could not follow the link to your photo.
– Roger HFeb 22 at 14:01

In Alaska it can last for several hours ( all night ), and depending on the month/season it can be at any time of the day or night. And then there is the alpenglow.
– Alaska ManFeb 22 at 17:26

Its duration is not exactly an hour and depends on location and date. Typically, it lasts between 30 mins (usually in the winter when days are shorter) and 2 hours (usually in the summer when days are longer). However, close to poles it may not happen, or it may last much longer when it is close to a solstice.

There may not be an exact definition, although I use Civil Twilight for my calculations based on experience. The main point is that during that time the brightness of the sky should balance with the reflectance of naturally illuminated objects. In other words, during the golden hour, the contrast between foreground and background (sky) is lowest. This is precisely why it is important in photography since this lets the most details be captured throughout a scene.

The second half of the morning and first half of the evening golden hour is characterized by warm light (golden) which is a result of the low angle of illumination of the sun. This is where its English name comes from.

The French, call it L'Heure Bleu which means Blue Hour from the first half of the morning and second half of the evening of the golden hour which is characterized by a deep blue sky resulting from indirect illumination of the atmosphere. It is more pronounced in the East in the morning and in the West in the evening.

For a geeky explanation, think of a rainbow. The red, orange and yellow bands make up the outside bands, while blue, indigo and violet are inside. This indicates that the light wavelengths that make up the outside bands actually bend less than the inside bands. So as the Sun sinks lower on the horizon, the blue components are not hitting the earth where you are observing. So the light hitting you has proportionately more red, orange and yellow. As for why the first half of the morning and second half of the evening is more blue, I'd suggest that as the light isn't hitting the earth directly, perhaps the bluer components reflect off the atmosphere more readily than the redder components.